This invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well. More particularly, a method for sealing a void incompletely filled with a cast material comprises the placing of an expandable material in the void which is to be filled with cast material, the expandable material expanding into spaces which are not filled with cast material. The method is particularly suitable for sealing openings in an annulus round a cast-in casing as it is known from the recovery of petroleum. The invention also comprises a device for practicing the invention.
When cementing an annulus between a casing and a formation wall in a borehole, especially when approximately horizontal boreholes are involved, it can be very difficult or impossible to achieve complete filling of the annulus with a cast material.
One reason for this condition is essentially that a fluid present on an underside of the casing is difficult to drain completely. This fluid may include drilling fluid.
Fluid present in the annulus during the curing of the cast material, and in particular fluid present in the lower portion of the annulus, could form a channel along the borehole, which may extend so far that it connects different zones of the borehole.
It is obvious that channels of this kind are undesirable as an uncontrollable fluid transport may occur in the channel. For example, formation water from a zone may flow into a nearby petroleum-producing zone.
It is known to use an expandable material to shut off an annulus. For example, Norwegian Patent No. 312478 discloses a packer which is made using a swellable material. After the packer has been placed at a desired location, the material of the packer absorbs a fluid and thereby swells until it seals the annulus.